1. Field of the Invention
The present invention relates to a backflow isolator and capture system for a particle flow through apparatus which includes a unique valve operator and pump control, and more particularly, concerns a flow cytometer for determining one or more characteristics of particles flowing through the cytometer with such a backflow isolator to provide safety in connection with changing sample test tubes and cleaning the flow path. The method of isolating and capturing backflow is also a part of the present invention.
2. Background Description
There are a number of cell or particle analyzing devices using flow cytometer equipment and techniques which rely on hydrodynamically focused fluid flow through an analysis orifice where the specific characteristics of the flowing cells or particles can be determined. Flow analysis of particles has been used in the determination of the variety of characteristics of individual particles. This analysis is most useful in determining characteristics of cells for the collection of information which would aid in areas of research, hematology, immunology and the like. The researcher, for example, could be interested in determining specific characteristics of the individual cells where those cells need to be classified, identified, quantified and perhaps sorted for further investigations or analysis.
One commercially available flow cytometer which relies on a hydrodynamically focused fluid system is known as the FACScan.TM. instrument sold by Becton Dickinson Immunocytometry Systems, Mountain View, Calif. The FACScan.TM. instrument rapidly analyzes cells on the basis of fluorescence and light scatter properties. Analysis is accomplished by introducing cells in suspension to the center of a focused liquid stream and causing them to pass, one at a time, through a focused light from a high power lamp or laser. Each cell is individually characterized by its light scatter signals and by the intensity and color of fluorescence emitted while it is illuminated.
In the aforementioned flow cytometer, a sheath liquid focuses the particles or cells as they pass through the orifice associated with the analyzing or counting capabilities. U.S. Pat. Nos. 4,503,385 and 4,526,276 describe particle analysis systems in which particles flowing in a stream are enveloped in a sheath liquid which focuses and confines the sample liquid (with the particles or cells) to the center of the flowing stream. U.S. Pat. No. 4,110,604 describes a particle density measuring system in which particles flowing in a stream are enveloped in a sheath liquid which focuses and confines the sample fluid (with the particles) to the center of the flowing stream.
In the presently known and available flow through equipment, electrically operated pumps, syringe pumps or the like are used in the fluidics of the system to move the liquid and particle flow through the flowcell analysis orifice and passageways. The usual operation for these pumps is to force or draw liquid with particles from a sample test tube through a sample capillary uptake tube centered in the sheathing liquid flowing in the direction of the particle analysis orifice. The Assignee of the present application has co-pending applications, U.S. Ser. No. 866,003 filed May 22, 1986, disclosing a housing for a flow cytometer with a particle unclogging feature and U.S. Ser. No. 125,095 filed Nov. 25, 1987 disclosing a sheathed particle flow controlled by differential pressure.
Particle analysis instruments often use air pressure to cause particle flow from a sample containing test tube into an analysis region of the instrument where a pressurized ensheathing liquid hydrodynamically focuses the particle stream for passage through the analysis region. Upon removal of the sample containing test tube the ensheathing liquid and particles can backflow through the sample uptake tube and drip off the end thereof. With certain samples dripping liquid and particles present a posslble biohazard. In particular, the sample can include potentially biohazardous cells which could drop, splatter and contact the operator or the work area. The air pressure used to drive the particles up the uptake tube has to be safely vented to avoid release of aerosols containing potentially biohazardous cells. This is a particularly great problem when removing the sample containing test tube which often contains residual air pressure in addition to the sample. Another concern is the possibility of the air pressure supply for the sample containing test tube causing the test tube to be unexpectedly blown off the flow cytometer housing.
With the foregoing in mind, improved techniques for safely handling the changing of sample containing test tubes in particle flow through equipment are still being sought. Such improvements in test tube handling should preferably be included in the particle flow through apparatus so that there are no biohazardous particles, vapors or liquids released. It is toward such an improvement that the present invention is directed.